1. Field of the Invention
The present invention relates to an anti-theft device for automatically hoisting or striking a flag on a carrying structure and in particular, although not exclusively, on a vertical support pole.
2. Description of the Prior Art
The conventional ways of hoisting a flag at the end of a pole are known, and which most generally consist in providing a pulley at the top of the said pole, in the groove of which pulley there passes a halyard equipped at the end with a shackle or other similar means for fastening to an eyelet made in the upper corner of the flag to be hoisted, this halyard which extends along the pole being, if necessary, returned by another pulley mounted at the base of the latter, so as to be connected at its opposite end to the lower corner of the flag. According to the direction of traction exerted on the halyard which is suitably tensioned between its two pulleys, it is thus possible to raise or lower the flag along the pole, the halyard thus forming a continuous loop.
Now, this well-known and notably simple system has the drawback that the halyard is accessible at the outside of the pole at any moment and that the flag hoisted on the latter may be struck, or even removed by a malevolent third party, who has only to move the halyard so as to lower the flag before separating the eyelets for attaching the latter relative to the ends of this halyard.
In order to overcome this drawback, it has already been provided to arrange the halyard, and in particular the two strands of the latter which move in opposite directions in the groove of the pulley provided at the upper part of the pole, inside a groove or a housing made actually inside this pole, the second pulley provided at the base of the pole and the parts of the halyard which roll up on the pulley being accessible via a hatch provided in the surface of the pole, this hatch normally being closed by a pivoting door which can be locked and which can only be opened by a user who has the key to open this hatch.
However, this solution is still not entirely satisfactory, since unauthorised unlocking of the hatch in general does not present any difficulties which cannot be overcome, so that the halyard may be controlled in the direction which strikes the flag and the latter can then be easily stolen or changed in an untimely fashion.